The apparatus concerned here is, in theory, one known as an indirectly fired anchor gun in which a flyweight, intended to drive a tack, an insert, or any other similar fastener, is propelled forwards under the action of the combustion of the charge of powder or the explosion of a flammable mixture of gases.
The fastener guide is more generally known as tack guide. This guide is often separate from the barrel and mounted in front of the barrel. Sometimes, the front part of the barrel acts as a tack guide, and, in this case, it is the entire barrel which is designed to be moved backwards as the apparatus is pressed against something, in the context of bearing safety.
As far as the safety shoe is concerned, when there is no fastener in the barrel, a spring pushes it towards the axis of the barrel into the retreat path of the tack guide, thus preventing the latter from retreating. This safety shoe has been designed to avoid the apparatus being operated empty, as this would be detrimental, firstly because practically all the firing. energy would be absorbed by the apparatus itself, but also because of the risk that the flyweight might penetrate the support material.
As for the loader, it has a push-rod for introducing fasteners into the barrel of the apparatus one by one, with a tell-tale of the advance of the push-rod.
However, when the push-rod of the loader has reached its extreme position, furthest forward in the loader, that is to say has reached the last fastener, the push-rod advance tell-tale is unable to determine whether or not there is still a fastener in the barrel, that is to say whether or not this fastener has already been used.